• Over 500, including university professors and business leaders, detained in Srinagar, Baramulla and Gurez
• ‘Worried about the safety of the Kashmiri children and women,’ tweets Malala Yousafzai
• Activist files petition before Supreme Court challenging curfew in Kashmir

Pakistan halted its main train service to India on Thursday and banned Indian films as it kept up the diplomatic pressure on New Delhi for revoking the special status of Kashmir, the region at the heart of 70 years of hostility between them.

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Federal Minister for Railways Sheikh Rashid Ahmad says the Express, or Friendship Express, train services are suspended from Thursday.

Kashmir remained under a communications blackout on Thursday with mobile networks and Internet services suspended and at least 300 politicians and separatists in detention to prevent protests, according to police, media and political leaders.

Kashmir's leaders have warned of a backlash and Pakistan, which also lays claims to the territory, vowed to fight for the rights of people living there.

"Pakistan is looking at political, diplomatic and legal options," Foreign Minister Shah Mehmood Qureshi told a news conference in Islamabad, though he ruled out a new military conflict.

"We're not looking at the military option. We're not," he said. The nuclear rivals have twice gone to war over Kashmir and fought an aerial duel in February.

The latest move comes a day after Pakistan downgraded its diplomatic ties with India and suspended trade in response to New Delhi's decision to reduce the special status of Kashmir, a Himalayan region claimed by both countries.

The opposition leader Ghulam Nabi Azad. File Photo

The railway suspension announcement was made as passengers were waiting to board a train in the eastern city of Lahore to travel to India.

Meanwhile, ANI news agency reported that the leader of the opposition in the upper house, Ghulam Nabi Azad from the Congress party, was stopped at Srinagar airport when he flew to the city and sent back.

Also, university professors, business leaders and activists were among the 560 people rounded up by the Indian authorities in midnight raids.

The detentions came as Prime Minister Narendra Modi was set to address the nation on the radio later on Thursday to explain his Hindu nationalist government's decision.

India on Thursday dismissed Pakistan's "alarmist" reaction to its decision to strip Kashmir of its autonomy, and warned its nuclear-armed rival against interfering in what it insisted was a purely internal matter.

India revoked Kashmir's special status in the constitution on Monday and brought it under its direct rule.

Pakistan responded by downgrading its diplomatic ties with India on Wednesday, announcing that it would expel the Indian envoy and suspend trade as the row between the neighbours deepened.

A Pakistani woman (left) embraces her Indian relative ahead of departure to India via the Samjhauta Express train in Lahore. AFP

The countries have fought two wars over Kashmir.

In a statement the foreign ministry said its decision was "entirely the internal affair of India".

"Seeking to interfere in that jurisdiction by invoking an alarmist vision of the region will never succeed."

New Delhi added that the move would boost economic development in the Himalayan region.

"The government of India regrets the steps announced by Pakistan... and would urge that country to review them so that normal channels for diplomatic communications are preserved," the statement added.

The diplomatic spat came as a petition was filed with the Supreme Court by an activist challenging the curfew in Kashmir, which was imposed to suppress any unrest in response to the loss of autonomy.

Activist Tahseen Poonawala and lawyer M.L. Sharma asked the Supreme Court to lift the lockdown and release people who have been detained as part of the crackdown.

Pakistani Nobel laureate Malala Yousafzai. File photo

Pakistani Nobel laureate Malala Yousafzai, who was shot in the head by the Taliban in 2012, on Thursday tweeted, that she was "worried about the safety of the Kashmiri children and women, the most vulnerable to violence and the most likely to suffer losses in conflict.”

"I believe we all can live in peace," she added, in comments that were supported and criticised by Twitter users from India and Pakistan.

No phone calls, no groceries

An unprecedented security lockdown amid a near-total communications blackout entered a fourth day on Thursday, forcing some news organisations to hand-carry dispatches out of the region.

In central Srinagar, the region's main city, few pedestrians ventured out of their homes to navigate barbed-wire checkpoints guarded by helmeted soldiers in camouflage, wielding rifles and protective shields.

Shopping malls, grocery stores and even clinics were closed. In previous security clampdowns, neighbourhood bodegas had opened their doors for a few hours a day after dark so that people could buy basic necessities like milk, grains and baby food. It is not clear whether the stores have opened in the current crackdown. Residents are used to stockpiling essentials, a practice they've honed during harsh winter months when roads and communications lines are often snapped.

Hundreds detained

University professors, business leaders and activists were among the 560 people rounded up by authorities and taken to makeshift detention centres – some during midnight raids – in the cities of Srinagar, Baramulla and Gurez, the Press Trust of India and the Indian Express reported.

Indian activists shout slogans against the government revoking Kashmir's special constitutional status in New Delhi on Wednesday.

Tens of thousands of Indian troops are enforcing the lockdown which includes no internet or phone services, and are allowing only limited movement on streets usually bustling with tourists flocking to the picturesque valley.

Experts warn that the Valley is likely to erupt in anger at the government's shock unilateral move once the restrictions are lifted, which could come on the Muslim festival of Eid on Monday.

Late Wednesday India's aviation security agency advised airports across the country to step up security as "civil security has emerged as a soft target for terrorist attacks" on the back of the Kashmir move.

Agencies